The present invention generally relates to a method for manufacturing a GaN semiconductor light-emitting element.
In the process of manufacturing GaN semiconductor light-emitting elements, a GaN compound semiconductor layer is generally formed on the C plane of a sapphire substrate. In the GaN compound semiconductor layer epitaxially grown on the C plane of the sapphire substrate, its top face corresponds to the C plane and its side face corresponds to the A plane. That is, the top face of the GaN compound semiconductor layer is parallel to the {0001 } plane of the GaN compound semiconductor crystal, and the side face of the GaN compound semiconductor layer is parallel to the                {1 1 2 0}planeof the GaN compound semiconductor crystal. Hereinafter, such a crystal plane is designated for convenience as the “{11-20} plane”.        
Furthermore, in this specification, in a hexagonal system, for example, the following crystal planes:                {h k ī l}plane        {h k i l}planeare designated for convenience as the {hk-il} plane and {h-kil} plane, and the following directions:        <h k ī l >direction        <h k i l >directionare designated for convenience as the <hk-il>direction and <h-kil>direction.        
In the case of a light-emitting diode (LED) in which a first GaN compound semiconductor layer of a first conductivity type (e.g., n-type GaN layer), and an active layer composed of InxGa(1−x)N, and a second GaN compound semiconductor layer of a second conductivity type (e.g., p-type GaN layer) are stacked, the lattice constant of the InxGa(1−x)N crystal is slightly larger than the lattice constant of the GaN crystal. In such a case, when the top face of each of the first GaN compound semiconductor layer, the active layer composed of InxGa(1−x)N, and the second GaN compound semiconductor layer stacked corresponds to the C plane, the active layer is subjected to compressive stress, and thus piezoelectric spontaneous polarization occurs in the thickness direction of the active layer. As a result, phenomena, such as a shift in wavelength of light emitted from such a light-emitting diode, a decrease in luminous efficiency, and an increase in operating voltage, and saturation in luminance, may occur.
On the other hand, when the top face of each of the first GaN compound semiconductor layer, the active layer composed of InxGa(1−x)N, and the second GaN compound semiconductor layer stacked corresponds to the A plane, the active layer is not subjected to compressive stress. Consequently, piezoelectric spontaneous polarization does not occur in the thickness direction of the active layer (for example, refer to Japanese Unexamined Patent Application Publication No. 2003-158294 (Patent Document 1)).
When an active layer composed of InxGa(1−x)N, the top face of which corresponds to the A plane, is formed by crystal growth, it is generally difficult to set the subscript x in the InxGa(1−x)N composition at a desired value because the incorporation of In atoms into the active layer is low. That is, in the active layer whose top face corresponds to the C plane, since three nitrogen (N) atoms are capable of bonding to one gallium (Ga) atom present in the top face during crystal growth, there is a high probability that any of the three N atoms capable of bonding to one Ga atom will be replaced with an In atom. On the other hand, in an active layer whose top face corresponds to the A plane, since only two N atoms are capable of bonding to one Ga atom present in the top face during crystal growth, it is one of the two N atoms capable of bonding to one Ga atom that will be replaced with an In atom, and the probability of replacement with the In atom is low in comparison with the case of the active layer whose top face is the C plane. Thus, the incorporation of In atoms into the active layer is low. As a result, it is difficult to obtain a light-emitting diode which emits light at a desired wavelength.